1. Field of the Invention
The present invention relates to a traveling wave amplifier (hereafter denoted as TWA) to drive, for instance, an optical modulator.
2. Related Background Art
Various types of TWAs have been disclosed in, for instance, Japanese Patent Applications published as JP-H10-510970, JP-2003-304131A, JP-2006-054765A, and/or United States patents, U.S. Pat. No. 5,550,513 and U.S. Pat. No. 7,368,997. A TWA ordinarily provides a plurality of amplifiers connected in parallel between input transmission lines and output transmission lines. An output of the TWA adds outputs of respective amplifiers by aligning their phases, or a delay from the input terminal to the output terminal, at the output terminal of the TWA.
When such a TWA is applied to be used as a driver, for instance, to drive an optical modulator or a semiconductor laser diode, the optical output provided from the optical modulator, or the laser diode, makes dull in the leading and falling edges of the optical output. Degradation in the edges in the optical signal becomes distinguishable when the operating speed of the TWA reaches, or sometime exceeds 10 Gbps in spite of an efficient use of a TWA in high frequency applications. A direct drive of the optical device by the TWA has been a practical technique.